1. Field of the Invention
The present invention relates to a silicon wafer and a method for producing the same. More specifically, the present invention relates to a silicon wafer (mirror surface wafer) obtained by doping nitrogen and hydrogen, and polishing (mirror fabrication) having a void region, and a method for producing the same.
2. Background Art
A silicon wafer used as a substrate for semiconductor integrated circuits (a semiconductor device) is cut from a silicon crystal, and the most widely adopted method for producing this single crystal is growth by the Czochralski method (hereafter referred to also the “CZ method”). The CZ method is a method for growing a single crystal by contacting a seed crystal with molten silicon in a quartz crucible, and slowly withdrawing it, by means of which a large size single crystal with few defects and without dislocations has been produced.
The semiconductor device is commercially produced by pulling the single crystal by using the above CZ method, using a wafer obtained from this single crystal silicon (an as-grown wafer) as a substrate, and subjecting it to many processes for circuit formation. In such a wafer, grown-in defects generated by aggregation of point defects during crystal growth are present. Exposure of these defects at the wafer surface has raised a problem, due to deterioration of the characteristics of a device formed thereon.
In order to produce a wafer having decreased density or decreased size of such grow-in defects, various approaches have been tried. First, JP 3255114 has disclosed technology, wherein, in producing a silicon wafer, pulling speed is set within a predetermined range, and nitrogen concentration for doping during crystal pull is set to be equal to or higher than 1×1014 atoms/cm3.
In addition, JP-A-2006-312576 has disclosed technology, wherein, in producing a silicon crystal, nitrogen in the aforesaid single crystal is set to be 1×1012 to 5×1014 atoms/cm3, and a hydrogen partial pressure in the gas atmosphere inside a growth apparatus is set to be 40 to 400 Pa. In addition, it has been disclosed also that defect regions are an oxidation-induced stacking fault (hereafter referred to also simply “OSF”) region, a Pv region (a defect-free region with vacant holes predominant, so-called “vacancies”) and a Pi region (a defect-free region with inter-lattice elements (“interstitials”) predominant).
According to the production methods of JP 3255114 and JP-A-2006-312576, there exist no voids (holes) in the OSF region of a silicon crystal doped with nitrogen (which hereafter may be referred to simply as a “nitrogen doped crystal”). However, such an OSF region has a low index showing absence of a crystal defects, which deteriorates the voltage resistance characteristics of an oxide film, that is, C-mode (a true destruction region) characteristics (high C-mode pass rate). In addition, in such a nitrogen doped crystal, a region with relatively low void density (specifically, a region in the nitrogen doped crystal having a void density of over 1×103/cm3 and equal to or lower than 5×103/cm3), also has low C-mode characteristics. In conclusion, the nitrogen doped crystal obtained by JP 3255114 cannot be said to have high C-mode characteristics totally, and is inferior in voltage resistance characteristics of an oxide film. This means that voids or some kind of microdefects are present over all of the aforesaid nitrogen doped crystal, which renders the wafers unsuitable for use in fabricating semiconductor devices.